The prior art discloses a variety of pulse width modulator schemes for energizing gaseous discharge lamps. For example, in Dragoset U.S. Pat. No. 4,039,897, the conduction angle of 60 cycle A.C. is varied to maintain a preset power level by time integrating the difference between the circuit output signal multiplied by a multiplier factor and a reference signal. In Schmutzer et al, U.S. Pat. No. 4,132,925 the switching time of a series pass transistor is controlled to provide a pulse width modulated chopped D.C. signal for energizing a lamp. In Holmes U.S. Pat. No. 4,170,747, two transistor pairs are utilized to provide a high frequency variable duty cycle energization signal to a high intensity discharge (HID) lamp. In Japanese Kokai No. 52-988, a high frequency, pulse width modulated push-pull transistorized inverter is used for lamp energization.
While the prior art teaches a diversity of approaches for energizing gaseous discharge lamps, the present invention is directed to circuitry for advantageously energizing fluorescent lamps in an energy-efficient manner. The circuitry of the invention provides a dimming capability which can be operated either manually or automatically as well as controls which are connected in a low voltage portion of the circuitry, thus permitting the use of less expensive low voltage control wiring.